Simulation And Experimental Research Of The Thermal And Moisture Environment In A Passive Greenhouse

Passive greenhouse with compacted soil wall as the enclosure structure is an original greenhouse type which is widely used in China. This type of greenhouse could take full advantage of the thermal stability of soil and wall, and could meet the growing need of plants without supplying assistant heating facility. Taking soil as the enclosure structure material is suitable for the passive greenhouse, for it is convenient, easy to get and low in construction cost, which has produced considerably economical and social benefits in China agriculture. But this kind of greenhouse comes from practice, and it is lacking of theoretical instructions about administration and regulation, so there are many problems remained to be solved, such as the thermal and moisture environment is not good, the insect disease of plants is terrible and the quality of fruit and vegetable is not excellent and so on. So carrying synthetic research about the thermal and moisture environment is very important to the environment optimization for plants.Adopting theoretical analysis, numerical simulation combined test as the main method, this subject established an unsteady tri-dimensional heat and water transport model of a passive greenhouse, explored the distribution law of indoor thermal and moisture environment, which supplied guidance for greenhouse environment management and tri-levels regulation and control theory.Proper test was taken to the typical soil-walled passive greenhouse in Jinan of Shandong province, parameters including outdoor solar radiation, temperature, relative humidity, heat flow, soil temperature and water content were tested. The test result shows that the heat insulation and reserve effect is excellent for this type of greenhouse; the indoor temperature is enough to maintain the growing of plants without disaster weather outside; the relative humidity at night is a little higher, so regulations should be taken to avert the plant disease.Took the test greenhouse as an original model, with proper simplifications and assumptions, established an unsteady tri-dimensional heat and water transport model, adopted the solid and fluid coupled solution method, study of heat and water reserve properties of wall and soil on indoor heat and water transport under complicated conditions was carried on; established water transport model caused by heat transport; discussed the dry air and vapor transport course between indoor air and porous soil media; took CFD computational way to solve the temperature and relative humidity field of indoor greenhouse. According to the previous work, theoretical support was supplied to complete this kind of passive greenhouse. The simulation result and test data matched well with an average absolute temperature error of±0.54℃and a fitting degree of 99.62%; an average absolute relative humidity error of±1.25% and a fitting degree of 99.83%; both of these two parameters got high reliability with a 95% basic reliability interval which verified the feasibility and veracity of the model.Several manual solutions about greenhouse management, regulation and control were offered from three levels according to the test and the simulation results, air level, plant level and soil level, which completed the traditional regulation and control method.